Cable and method of making the same



y P. H. CHASE. l CABLE AND METHODU 0F MAKING THE SAME. APPLICATION FILEDILOV- 2, IQIGAIIENEWED AUG. 9, 1920.

I Patented Mar. 8, 1921;

@a1/@OHM nue/WISO@ 3&9 his @Hoa/mags UNITED "STATES PATENT oi-Flea4PHILIP H. CHASE, OF CYNWYID, PENNSYLVANIA.

CABLE AND METHOD OF MAKING THE SAME.

of Cynwyd, in the county of Montgomery fand State of Pennsylvania, haveinvented an Improvement in Cables and Methods of Making'the Same, ofwhich the following is a specification. n

This invention relates to electrlc; cables, and with regard to certainmore specific features, to cables for high-voltage power work.

Among the objects of the invention may be noted the provision` of asimple andimproved method ofconstructing a cable to relieve or equalizethe dielectric stressesv and to decrease the dielectricl losses incidentto high-voltage work; the provision of a cable lso constructed as tominimize the eddy currents and other disadvantagesdue to .currentsinduced by the alternating currents flowing through the yconductors ordue to short-circuit f currents; the provision of a cable constructed tofacilitate the vconduction of heat from the interior of the cable to theexterior thereof; the provision of an efficient and durable sheathsubstantially continuous for the purpose of permitting materialequalization or dissipation of electrostatic stresses and decrease ofdielectric losses, and

likewise substantially continuous and offering a lowresistance to thepassage of heat from the interior fof the cable toward the, eX-

terior thereof, but offering a material and yeffective resistance ftothe flow of eddy cur'- rents and any other deleterious currents, whichmay be refererd to as electrodynamic currents to distinguish them fromthe electrostaticstresses and 'losses in the cable; and the provision ofa stress7relieving`-sheath having preferably a high fusing point andample mechanical strength to :prevent 1njury or breakage if the cableA1s bent, and

v having sufficient heat-conductivity, heatstorage capacity, andheat-radiating power to minimize the danger of fusing of the sheathduring short-circuit conditions.l i

Other objects will be in part obvious and in ypart pointed outhereinafter.

The invention accordingly `comprises the. features of construction andoperation, 'combinations of elements, arrangements of parfts, steps andsequence of steps which are exemplified in the structure hereinafterdescribed and the scope of the application of ,which will ybe indicatedin the following claims.

In the accompanying drawings, 1n which Specification 'of Letters Patent.

Patented Mar. 8, y1921.

' Apilication led November 2, 19"16,`Seria1 No. 129,218. Renewed August9, 1920.' Serial No.` 402,299.

are shownY one or more of various possible embodiments of the invention,

Figure 1 is a perspective of a conducto with its layer of insulation,showing a sheath in the form of a tape being wound around saidinsulation.

Fig. 2 is a face view of modified forms of tape. I

Fig. 3 is a similar view of other modifications.

Fig. 4 is a view similar to Fig. 1, showing a sheath in the form of aninsulating tape covered with conducting foil.

Fig. 5 is an enlarged section on the line Fig. 6 is a face view of amodified form of conducting foil on insulating tape such as used in Fig.4.

Fig. 7 is a transverse section through a 'three-conductor cable, showingone embodiment of my invention applied thereto.

Fig. 8 is a similar sectlon through a threeconductor cable ofV thesector type.

Fig. 9 is a sectional view of a modified form of three-conductor cable.

Similar reference characters indicate similar parts throughout theseveral views of the drawings. Y

In considering this invention in its relation to the prior art, it maybe noted; that with the increasing use of electric cables, especiallycables for three-phase alternating current at high voltages and oftenfor heavy currents, there has been an increasing appreciation of thelosses-and deficiencies incident to thepassage of high-voltagealternating current through conductors in close proximity to oneanother, as in cables. Many attemptshave been made to classify thelosses and deficiencies with a view to discovering the factors affectingthem, and a number of methods and arrangements have been devised forconstructing cables in such a lway, as to reduce these losses anddeficiencies singly or together. The present invention provides afmethod and cable construction designed to minimize the several losses,coincidentally with minimum accompanying disadvantages, and formultipleconductor cables to increase the carrying capacity for a giventemperature difference between the interior. and exterior thereof. Asthe description progresses, it will be seen. that the requirements ofefficiency, low cost, mechanical strength and durability under abnormalservice conditions, are adequately met in the method and apparatus ofthe present invention.

The present invention contemplates the provision of a mechanicallydurable conductor so constructed and positioned within the cable as tofacilitate the equalization or dissipation of stresses of anelectrostatic nature, at the same time minimizing the heating and otherdisadvantages due to the flow of currents, for instance eddy currents,which may be said to be of an electrodynamic nature, and, particularlyin the case of multiple-conductor cables, affording a path of lowthermal resistance from the heated interior of the cable toward the eX-terior thereof, for the purpose of reducing the temperature within thecable for a given load, or permitting a greater load to be carriedwithout increase of the internal temperature.

This three-fold object, of reducing electrostatic stresses and losses,electrodynamic losses, and heating, is preferably attained by windingaround the insulation individual to the conductor or to each conductor,a conducting sheath offering (l) a path of low resistance to the fiow ofcurrent due to electrostatic potential differences, (2) a highresistancepath or series of paths for the electrodynamic currents, such as eddycurrents, and (3) a path of low thermal resistance for conducting awayfrom the interior of the cable the heat generated therein. The sheathmay extend only partly around the periphery of the conductor in certaincases, but preferably extends all around the conductor. The sheath isnot intended primarily for mechanical protection, but for electrical andthermal purposes. In a threeconductor cable for three-phase alternatingcurrent, one of these sheaths is provided around the insulation`individual to each conductor, and the three sheaths are preferably incontact with a sheath external to the three conductors or with eachother when the conductors are formed into a cable. Belt insulation mayor may not be applied over the three conductors, before an outer sheathor covering is applied.

In order to facilitate the equalization of electrostatic stresses, thesheath is virtually electrically continuous peripherally, that is, in aplane at right angles or approximately right angles to the axis of theconductor. This equalizes the distribution of electrostatic stressesaround the periphery of each conductor.

The electrodynamic losses due to eddy currents formed in the sheath bytransformer action, are minimized by' laminating the sheath (that is,sectionalizing, or dividing the sheath at'short intervals of themagnitude of a fraction of a decimeter, and preferably of the magnitudeof a fraction of a centimeter) in planes at right angles or atapproximately right angles to the direction of the induced potentialdifferences causing these eddy currents, and providing between thelaminations either a space in the form of an open slit or corrodedsurfaces or varnished surfaces, or some other impediment to the flow ofcurrents across the barrier. If for mechanical reasons, as ispreferable, the laminating slits or perforations do not extend acrossthe entire width of the conducting tape which constitutes the sheath,some eddy currents may flow around the laminations, but the paths aroundthe laminations are so long that the resistance offered by thc pathswould effectively reduce this eddy current flow to a negligible value.In any event, the sheath is broken up into disconnected or partlydisconnected ele ments which still form a continuous sheath forelectrostatic purposes, but which break into small elements the pathsalong which the eddy currents would flow so that the inducedelectrodynamic voltages acting in each element have to forcethe eddycurrents through a comparatively long, high-resistance path or paths. Asa result, there is a reduction in the magnitude of the eddy currents andin the resultant power losses and heating from these causes as well. Theborders and other unbroken longitudinal portions obviously ofler acomparatively great resistance to the passage of large currents,through. the metal coverings, lengthwise of the cable.

The heating of a multiple-conductor cable is reduced because the `sheathoffers a virtually t ntinuous path around the periphery of the insulatedconductor; and since the sheath may be as thick as desired withoutinvolving excessive electrodynamic losses, the sheath may be made thickenough to offer a path of low thermal resistance for the rapidconduction of heat from around the insulated conductor in the centralparts of the cable toward the outside sheath.

Copper, for instance, has over three thousand times the heat-conductingcapacity of impregnated paper such as is often used in high-tensioncables. Therefore the six metallic paths from the interior of athreeconductor cable to the periphery relieve the insulation over theouter part of the conductors of considerable heat-conducting duty. Thetemperature of the insulation next the conductors and the averagetemperature of all the insulation are thereby decreased, or from anotherpoint of view, the cable can be safely and economically operated athigher currents and voltages than it could without this invention. Thereduction and equalization of the temperature of the insulation have amore than proportional effect on the dielectric losses, a factor of imjtend entirel portance in high-voltage cables, and also have an effect onthe break-down strength of conducting tape k3 provided with diagonallaminations 4 arran ed at such an angle to the longitudinal ax1s of thetape that the laminations are approximately perpendicular to the axis ofthe conductor when the tape is wound helically upon the insulation 2. Inorder that the tape may be continuous and thus easy to wind on theinsulation 2, the laminating slits referably do not exacross t e ta ebut are short enough to eave at the e ges of thetape margins or borders5. In this embodiment of the invention, the borders 5 of adjacent turnsof the tape overlap and are in contact with each other, to minimize the.thermal resistance of the sheath in a direction around the periphery ofthe insulation and to insure continuity for electrostatic purposes. Thisconstruction, moreover, insures some extent of overlapping even when thecable is bent. The eddy currents due to potential differ# ences in adirection axially of the conductor are kept at a minimumbecause theunobstructed paths axially of the conductor` are only as long as thewidth of each lamination, and through this short distance the potentialdifferences tending to set up the eddy currents will be negligible; andthe eddy current paths also have long elements perpendicular to thedirection of the induced potential differences, resulting in limitingtheeddy currents to negligiblel values. In fact, the width of tape,width of` borders,

width of laminations, and pitch of the tape iin winding,`may be soproportioned as to keep the eddy-current losses downto an del sirablevalue, and this without sacri cing mechanical strength of tape orcontinuity of surfaces for equalizing electrostatic stresses, or lowthermal resistance around the periphery of the sheath, for conductingheat to the exterior portions ofthe cable. By providing a sheath that ismechanically strong, the danger of'rupture or injury during manufactureor installation oroperation, is minimized. v

By providing such laminations at right angles to the axisof theconductor, the

sheath offers a comparatively high impediment to the passage of currentsinduced by short-circuit currents in the conductor.v The sheath,moreover, has large heat-dissipating' surfaces and heat-storagecapacity, and thus the sheath is protected from fusing that might occurdueto the heating effect ofY The central portion 16 may bereplaced by.dling the tape during the winding operation. Margins or borders 15,similar to the borders 5 ofthe tape 3, are also provided.

laminations keyed at one or more points, as indicated at 17 such a tapecombines the advantages of the tape shown in Fig. l, withv greatermechanical strength. In Fig. 3, the tape 23 is provided with marginsv orborders 25 and diagonal unbroken ortions 26, between which are thediagonaldaminations 24. The unbroken portions 26 may be replaced bylaminations keyed at one 'or more points, as indicated at 27. l

In Fig 4, the insulation 32 surrounding the conductor 31, has woundhelically upon it 7an insulating tape 37 to which is secured a metaltape or/foil 33 which, like the tape 3 of Fig. 1, is provided withdiagonal laminations 3 4 arranged at such an angle to the longitudinalaxis of the foil that the lami. nations are approximately perpendicularto the axis of the conductor when the insulating tape and the rfoil arewound helically upon the insulation 32, the margins or borders 35 beingprovided to add mechanical strength to the foil and t0 facilitate thehandling of it during its manufacture and application to the insulatingtape and to the conductor. The tape or foil may be the full width oftheinsulating tape and it may or may not be found preferable to cement orotherwise cause the foil to adhere to the in- 105 sulating tape. Asshownin the enlarged section in Fig. 5 the laminations 34 are separatedlaterally by open slits or lperforations serving to separate the foil oneither side of the slit, or the slits may be made and again closed afterthe adjacent surfaces have been corroded, oxidized,v or varnished, orotherwise insulated from one another to an extent sufficient vtomaterially decrease or prevent the passage of eddy currentsbetweenlaminations.4

In Fig. 6, there is illustrated a metal foil 43 carried upon aninsulating tape 47, the laminations 44 and borders 45 resembling thelaminations 14 and borders 15 of Fig. 2. 120

'In applying the tape or foil to the insulated conductor of the severalmodifications herein disclosed, the foil may be wound on at the sametime as the insulating tape, or the two maybe wo-und separately, and inthe latter case, the insulating tape may be laid with any desired pitchcompared to the pitch of .the foil, or may even be applied with thelongitudinal axis of the tape parallel to the axis of the conductor; andthe foil may likewise be applied with its longitudinal axis parallel tothe axis of the conductor, or may surround all or part of the peripheryof the insulated conductor. And there may be provided a protecting tapeapplied outside the foil to protect the foil from mechanical abrasion;this protecting tape, however, for multiple-conductor cables, shouldpreferably not cover the entire surface of the foil, and should be thinenough to permit contact between the tapes or foils applied to each ofthe conductors and between each foil and the external sheath. lVhen thefoil is laid on after the insulating tape has been applied to theconductor, the foil strip is preferably wound with a pitch less than itswidth, so that adjacent edges over- I lap in the manner indicated inFig. 1, to

insure overlapping when the cable is bent, and for the equalization ofelectrostatic stresses. This construction, moreover, provides alow-resistance peripheral path for the conduction of heat. Or a foil maybe applied with spaces between adjacent turns, and these spaces coveredby a second foil. Or the foil may be wound in two or more layers, but insuch an embodiment of the invention, the layers are preferably insulatedfrom one another to an extent sufficient to prevent eddy currents fromflowing from one layer to another.

In Fig. 7, there is shown in transverse section a three-conductor cablewith the usual central and lateral filling bodies 55, and with thepresent invention applied to the cable. The conductors 51 are eachprovided with insulation 52 around which is laid the conducting sheath53, which may take any one of the forms above described. The threesheaths 53, it will be noted, are at substantially the same electricalpotential because they may be in contact with one another or with thebelt-sheath 56, which may be provided if desired, and may or may not belaminated. The belt insulation is indicated at 54. The belt-sheathassists in the Idistribution of heat around the periphery of the cableand thus increases the conduction of heat to the external sheath. Theeddy currents due to the varying or rotating magnetic field caused bythe currents in the conductors, are broken up or minimized bylaminations similar to those illustrated in Figs. 1 to 6. The heatgenerated in the interior of the cable, due to IZB losses in theconductors, to losses in the insulation, and to losses in the pathstaken by the eddy currents, isreadily conducted toward the externalsheath 58 of the cable by means of these sheaths 53, so that the cablecan be operated at a lower internal temperature for the same current orat a higherl current for the same internal temperature.

In Fig. 8, there is illustrated a three-conductor cable of the so-calledsector type, in

which the conductors 61, instead of being round, are in the form ofapproximately K120--degree sectors, and each insulated conductor issurrounded with a sheath, the whole being covered by an overall sheathwithout belt insulation. The central and lateral filling bodies areindicated by the reference numeral 65. In such a cable, the radiation ofheat becomes a more important factor, and it will be noted that byapplying the present invention to a cable of this type, the problem ofheat conduction can readily be simplified by making the sheaths 63 heavyenough to afford a path of sufficiently low thermal resistance for theconduction of heat to the exterior of the cable. It is evident from theforegoing description, that the sheaths 63 may be omitted from most, ifnot all, of that part of the periphery of the individual conductorswhich is in contact with the external sheath 68, without sacrifice ofthe benefits of this invention. The other losses incident t0 theemployment of sector cables are likewise reduced by the application ofthe present invention thereto, since the conducting paths of the severalsheaths G3 and from one sheath to another in a (lirection at rightangles to the axis of the cable, facilitate the equalization ofelectrostatic stresses, while the laminations in the sheaths prevent theformation of troublesome eddy currents.

In Fig. 9 is illustrated a further means of assisting the conduction ofheat from the central portions of the cable to the external 1.

sheath 78. This means comprises heat-conducting sheets 79 around part ofthe periphery of the external sheath and provided with vanes 80extending from the external sheath radially inward between theconductors 71 toward the central portions of the cable. These vanes arepreferably laminated, as indicated in Fig. 9, to minimize eddy-currentlosses. A laminated sheath 73 individual to each conductor may beprovided, as in the preceding embodiments of this invention. Thecustomary central and lateral filling bodies are provided, as indicatedat 7 5.

Instead of having the conducting sheath laid on the outside of theinsulation individual to a conductor, the sheath may be embedded in theinsulation surrounding the conductor. for such purposesv as grading ofthe insulation. Many if not all of the advantages incident to the use ofthis invention in a sheath outside the insulation may be attained byapplying the invention to such an intermediate sheath. Furthermore, itmay be advisable to have the intermediate sheath continuous for thewhole length of the cable in order to maintain the sheath at apredetermined potential, and it will be noted that an intermediatesheath constructed according to the present invention may i3' readily bemade electrically continuous throughout the length of the cable for thispurpose, without sacrifice of the advantages incident to its use.

From the above, it will be seen that the several objects of theinvention are realized, and other advantageous results attained.

As various possible embodiments might be made of the above invention andas various changes might be made in the embodiments above set forth, itis to be understood that all matter herein set forth or shown in theaccompanying drawings is to be interpreted as illustrative and not in alimiting sense.

Having thus revealed my invention, I claim and desire to secure byLetters Patent of the United States:

1. An electric cable combining a conductor, insulation around saidconductor, and,

a conducting sheath surrounding the conductor to facilitate thedissipation of electrostatic stresses, said sheath being slitted acrosspart of its Width to reduce currents therein.

2. An electric cable combining a conductor, insulation around saidconductor, and

a conducting sheath surrounding the con ductor to facilitate theequalization of electrostatic stresses' and the-conduction of heataround the periphery of the insulation, said sheath being perforatedacross part of its Width to decrease losses due to currents therein. y,

3. An-electric cable combining a conductprginsulation surrounding theconductor, and conducting material surrounding the insulation andaffording a Ypath or paths aroundthe insulation to equalize theelectrostatic stresses, said material being perforated across part ofits Width in a direction to break up currents therein.

4. An article of the class described, combining a conductor, insulationsurrounding said conductor, a protecting covering outside theinsulation, and conducting'material in the insulation and surroundingsaid conductor, said material affording a substantially continuousperipheral path for the relief of electrostatic stresses andhaving aseries of short relatively insulated paths axially of the conductor tooffer a comparatively high impediment to the passage .of eddy currents.

5. In a multiple-conductor cable, in combination, a body of conductingmaterial'covering the individual insulated conductorl and extendingaround such individual conductor to reduce electrostatic stresses andperforated across part of its Width in planes substantially at rightangles to the axis of the conductor, the material surrounding oneconductor being in electrical contact with the material surrounding anadjacent con ductor.

ving divided intoaxially short and relatively 6. In a high-tension cableincluding three or more separately insulated conductors', asubstantially. complete integument of conducting material covering theopposing faces of each of the assembled insulated conductors andextending substantially around said conductors to form an'Aelectrostatic shield, said material bein slitted across part of itsWidth and offering a comparatively loW-resis'tance path to the passagetherethrough of heat energy, but offering a comparatively highimpediment to the passage therethrough of eddy currents.

7. In a high-tension cable including three or more separately insulatedcnductors, a substantially complete integument vof conducting materialcovering the opposing faces of each of the assembled insulatedconductors, and extending substantially around said conductors andacting asA an electrostatic shield, said material offering acomparatively low-resistance path to the passage therethrough of heatenergy in Ia substantially peripheral direction but beinsulated sectionsin order to offer a comparatively high resistance to the passage of'eddy currents therethrough.

8. In a high-tension cable including three v or more separatelyinsulated conductors, a substantially complete integument of conductingmaterial covering the opposing faces of each of the assembled insulatedconductors andextending substantially around said conductors, saidmaterial acting as an 'electrostatic shield and offering a comparatively10W-resistance path to the passage therethrough of heat energy in asubstantially peripheral direction but offering a compar'atively'highresistance to the passage 105 of eddy currents therethrough; '9. As anarticle of manufacture, a conducting Web for electric conductors, saidweb being provided With laminationspso disposedj as to be 'substantiallycircumferential 110 of the 'conductor when the, web is applied thereto,the laminations extending only part Way across the Width of theWeb toprovide unbroken borders or margins at either side of the web` tofacilitate handling of said web.

10. As an article of manufacture. a conducting web for electricconductors, said I web comprising ian insulating tape and a n metal foilsecured thereto, the `lfoil being provided with laminations so disposedas to /be substantially circumferential of the con- I ductor when the.foil is applied thereto, the laminations extending only part way acrossthe width of the foil to provide unbroken 125 borders or margins ateither side of the foil.

11. As an article of manufacture, a metal foil for cables, said foilhaving laminations so disposed as tobe substantially circumferential ofthe cable conductor when the foil is applied thereto, the laminationsextending only part way across the width of the foil to provide unbrokenstrips at either side of the foil.

12. As an article of manufacture, a metal -foil for cables, said foilhaving laminations so disposed as to be substantially circumferential ofthe cable conductor when the :toil is applied thereto, the laminationsextending only part way across the width of the foil to provide unbrokenstrips at the lateral edges of the foil and longitudinally of the foilbetween .said lateral edges.

13. As an article of manufacture, a metal foil for cables, said foilhaving laminations so disposed as to be substantially circumferential ofthe insulated cable conductor when the vfoil is applied thereto, theedges of the foil at the laminations being provided with insulatingmaterial to offer substantial resistance to the passage of currentacross said laminations.

14. The method of makingr a cable, which comprises insulating aconductor and winding around the insulation a conducting tape providedwith laminations disposed at such an angle that said laminations are atsubstantially right angles to the directions of the potentials causingthe flow of eddy currents after the tape is applied, the edges of thetape overlapping to afford a continuous electrostatic shield for theconductor.

15. The method of making a cable, which comprises insulating a conductorand winding helically around the insulation a conducting tape providedwith laminations extending substantially across said tape and disposedat such an angle that said laminations are at substantially right anglesto the conductor after the tape is applied, the edges of the tapeoverlapping to afford a continuous conducting path circumferentially ot'the conductor, the laminations minimizing the formation of eddy currentsin the sheath.

16. The method of making a cable, which comprises applying an insulatingtape to an insulated conductor, winding helically upon said tape alaminated conducting web of metal foil oifering a low-thermal-resistancepath circumferentially of the conductor and a high-electrical-resistancepath axially of the conductor; and covering said web With asecond-insulating tape.

17. VThe method of making a cable, which comprises .winding helicallyupon an insulated conductor'an insulating tape with a laminatedconducting web of metal foil se-' cured thereto, and offering alow-resistance path circumferentially of the conductor and 60 ahigh-resistance path axially of the conductor; and covering said webwith a second insulating tape.

18. The method of making a multipleconductor cable which com risesapplying an insulated tape to each ot a plurality of insulatedconductors, winding helically upon each of said tapes a laminatedconducting web of metal foil offering a low-resistance path to heat and-a high-resistance path to eddy currents, assembling the conductors sothat the several webs contact with one another, and inclosing theassembled conductors in a protecting sheath.

19. The method of making a multiple-conductor cable which comprisesapplying an insulated tape to each of a plurality of insulatedconductors, winding helically upon each of saidtapes a laminatedconducting web of metal foil offering a low-resistance path to heat anda high-resistance path to eddy currents, partially covering each of saidwebs with a second insulating tape to protect the webs, assembling theconductors so that the several webs contact with one another, andinclosing the assembled conductors in a protecting sheath.

20. In a multiple-conductor cable, in combination, a conductor,insulation therefor, and a body of conducting material covering saidinsulation and extending around said conductor, and comprisinginterlocking laminations arranged in planes crosswise of the directionof the induced voltage.

21. In a. multiple-conductor cable, in combination, a body of conductingmaterial covering the individual insulated conductors and extendingaround said individual conductors and laminated in planes crosswise ofthe direction of the induced voltages, and a body of conducting materialsurrounding the conductors thus covered and serving to distributertheheat around the periphery of the cable.

22. In a multiple-conductor cable, in combination, a body of conductingmaterial covering the individual insulated conductors and extendingaround said individual conductors and laminated in planes crosswise ofthe direction of the induced voltages, and a belt-sheath surrounding theconductors thus covered and serving to distribute the heat around theperiphery of the cable and thereby increase the conduction of heat totheA external sheath, said belt-sheath being likewise laminated.

' In testimony whereof I have signed my name to this specification this2nd day of November, 1916.

PHILIP H. CHASE.

